The invention relates to a television circuit for the reduction of flicker on a display, for a picture signal whose picture information repeats itself in cycles of two consecutive field periods. The circuit includes, an input terminal having a delay device coupled to the input terminal producing a time delay equal to two or more whole field periods. A signal combining circuit is coupled to the input terminal and to an output of the delay device. A switching circuit is coupled between an output of the signal combining circuit and an output terminal for forming together combined picture signals having during field periods picture information originating from different field periods.
Such a television circuit is disclosed in the U.S. Pat. No. 3,886,589 more specifically for use in a so-called "field skip" signal storage and display device. Before signal storage is effected, the combined picture signals are formed with the aid of the delay device and the signal combining circuit. Of these combined picture signals alternate picture signals are stored (field skip) during field periods through the switching circuit. Signal storage may be effected every other field period. On display of the stored signal by the signal storage and display circuit the stored information is repeated once, in the subsequent field period. Thus, the television picture signal obtained contains picture information which repeats itself in cycles of two consecutive field periods with a possible step change of picture content therebetween. Forming the combined picture signals prior to storage according to the patent has for its object to effect a reduction in flicker phenomena on display in a display device of the step-changing picture signal.
In addition, the patent describes that a step-changing picture signal may be the result of a tele-cine conversion. Herein, when the cine film is displayed at a rate of 25 frames per second and with a field frequency of 50 Hz, the information associated with one cine film frame is not included in one field period of the picture signal but is repeated in the subsequent field period. FIG. 7 of the patent further shows that when a cine film is displayed at a rate of 24 frames per second and with a field frequency of 60 Hz, 12 frames out of the 24 frames are included, repeated alternately once and twice in 2.times.12+3.times.12=60 field periods. If thereafter, optionally, the described intermittently effected signal storage of combined picture signals is used, the storage and display circuit will produce during signal display an adapted step-wise changing picture signal.
Apart from the fact that in both cases flicker reduction is obtained to some degree by forming the step-changing picture signal to be displayed on a display screen prior to signal storage, and combining the picture signals over several field periods, the step-change following the repetition of information in the cycle will produce flicker. The patent does not propose measures to counteract this.